1. Field of the Invention
The present invention relates to fuel tanks, and more particularly to automotive saddle fuel tanks. Still more particularly, the present invention relates to systems for controlling filling of a fuel tank in a refueling procedure.
2. Background Art
Automotive saddle fuel tanks have a tank shell defining a bottom. The tank shell is configured with a centrally disposed bight in the bottom thereof. The bight provides an exterior concavity which is intended to provide accommodation for drive and/or exhaust components of the vehicle to pass freely therethrough. While providing free space at the exterior of the fuel tank, the bight also provides a riser interior to the fuel tank, in turn providing two sumps, namely, a primary sump and a secondary sump. The two sumps conjoin in the space of the fuel tank higher than the height of the riser. One example of such saddle fuel tanks is disclosed in JP2004-189074A.
By virtue of their saddle configuration, such fuel tanks are used primarily in relation to rear wheel drive motor vehicles. The tanks can be appropriately arranged over drive components or over parts of the exhaust system of the vehicle. For that purpose, as indicated above, the fuel tank has a concavity extending upwardly into the tank.
When the vehicle in which the saddle fuel tank is fitted is in an inclined position or in different conditions of acceleration, particularly when the vehicle is subjected to transverse acceleration forces in bends of a road, it is quite possible for fuel to flow over the riser from one sump into the other sump, thereby resulting in different filling levels in the sumps.
It will further be noted that differences in level between the sumps can give rise to problems when refueling the motor vehicle, particularly when the fuel in one sump of the tank reaches a level at which a refueling vent valve provided therein responds, although the maximum filling level has not yet been reached in the other sump. In this case, the automatic shut-off valve in refueling gun shuts off prematurely in the refueling procedure, with the consequence that the tank cannot be completely filled. This problem can occur in particular if the riser provided in the tank is particularly pronounced and the refueling vent valve shut-off level is below the level of the top of the riser, so that equalization of the levels in the sumps by fuel flowing across one sump into the other sump through a compensating or equalizing line could occur only after the refueling vent valve has responded.
For the purposes of equalizing the filing levels in various sumps in a saddle fuel tank, it would be possible to inter-communicate various sumps of a saddle fuel tank by way of compensating tube or conduit. It will be noted however that this involves ensuring the same filling level in different volumes of the sumps of the tank, both when the motor vehicle is stationary and also when it is in operation, although that may not always be desirable.
As a comparable arrangement for the purposes of equalizing the levels of fuel in different volumes of various sumps of a saddle fuel tank, it would be possible to use a compensating line in the form of a siphon. The compensating line communicates by way of a branch with a vacuum chamber of a suction jet pump which is operated by the return flow of fuel from the engine back to the tank. This arrangement ensures that any air or gas which has accumulated in the compensating line can be removed so that equalization of the levels of fuel in the various sumps of the tank can take place irrespective of fuel being removed by suction from the compensating line.
This design is disadvantageous however insofar as an identical level of fuel in each of the sumps of the tank is guaranteed only if the vehicle is not transversely inclined. If the vehicle is transversely inclined when the tank is being refilled, it is still not possible to ensure that the automatic shut-off valve in the refueling gun shuts off when the level of fuel in the sumps is the same. Such a design configuration suffers from disadvantages in terms of refueling.
FIG. 1 is a sectional schematic view of a saddle fuel tank 10 having a tank shell 12. The tank shell 12 defines a bottom 14 and an oppositely disposed top 16. A bight 18 at the bottom 14 provides a concavity 20 exterior to the fuel tank 10 and a riser 22 interior to the fuel tank 10, in turn providing a primary sump 24 and a secondary sump 26.
A tank filer pipe 28 provides an entry for fuel into the fuel tank 10, wherein the primary sump 24 is identified as the sump first filled by fuel introduced from the filer pipe 28. Although not shown, at least one fuel extraction system is disposed in the fuel tank 10. Such fuel extraction system is known and can be found for example in U.S. Pat. No. 6,832,602 B2 (Tanimura) to which reference may be made for a more detailed description and the disclosure of which is hereby incorporated into this specification. Means for venting the fuel tank 10 are in the form of a single common refueling vent valve 30 for the primary and secondary sumps 24 and 26. The vent valve 30 is disposed in the secondary sump 26 in fluid connection with an outwardly extending vent conduit 32 that runs to a vapor storage canister, not shown. Fuel vapors are routinely vented to the canister from which they are later purged by engine manifold vacuum and burned.
Immediately after movements of the motor vehicle causing fuel to flow over from the primary sump 24 into the secondary sump 26 when the vehicle is subjected to transverse acceleration, it is quite possible that the fuel in the secondary sump 26 reaches a level at which the refueling vent valve 30 responds, but the fuel in the primary sump 24 drops to a level far below the maximum filling level as shown in FIG. 2. In this case, the automatic shut-off valve in the refueling gun shuts off in the refueling procedure. As a result, the fuel tank 10 cannot be completely filled.